This application is related to oxygen sensors, methods of using oxygen sensors, and related systems for use with combustion processes, for example in internal combustion engines.
As known by those of skill in the art, the air:fuel ratio in combustion processes, particularly in internal combustion engines, is typically represented by lambda (λ), with λ defined as is the actual air:fuel ratio divided by the air:fuel ratio at the exact stoichiometric mixture. Thus, in mathematical terms λ=air:fuelactual/air:fuelstoichometric. Values less than 1.0 are fuel-rich (rich), values greater than 1.0 are fuel-lean (lean). For many internal combustion engines, maximum power is achieved around λ=0.86, and maximum fuel economy is achieved around λ=1.45-1.55. As can be appreciated, engine management systems typically focus heavily on controlling λ. As such, most large internal combustion engines have oxygen sensors to sense exhaust gas oxygen levels, with the data from the oxygen sensor used by the engine management systems for various engine management functions. For smaller internal combustion engines, such as those used in motorcycles, all-terrain vehicles, recreational marine applications, and unmanned air vehicles, the size constraints of the engines presents difficulties in identifying suitable oxygen sensors.
Fortunately, small resistive-based oxygen sensors are known, see, for example, U.S. Patent Application Publication 2011/0186446. Such oxygen sensors find a particular application in engine management control for small internal combustion engines. In addition, such sensors are useful for individual cylinder control in multi-cylinder engines and hybrid engines for automotive and off-road applications.
The 2011/0186446 oxygen sensor may be considered as a switching oxygen sensor with some unique properties. Such sensors have a drastic change (orders of magnitude) in the resistance of the sensor element when transitioning across the stoichiometric boundary in air:fuel ratio of Lambda (λ)=1.00. For example, for the n-type semiconductor version of the 2011/0186446 sensor, above this crossover point (in the lean region with λ>1.00), the sensor's resistance is very high and not significantly responsive to changes in the oxygen content in the gasses to which it is exposed; however, below this crossover point (in the rich region with λ<1.00) the resistance is significantly lower and has a positive relationship with oxygen content. Conversely, for the p-type semiconductor version of the 2011/0186446 sensor, the resistance is very high in the rich region, but is lower and has a positive relationship with oxygen content in the lean region.
While the 2011/0186446 sensors are useful for many situations, such as those described in the 2011/0186446 publication, there remains a need for alternative oxygen sensor arrangements, and for alternative methods of oxygen sensing and controlling combustion processes based on the sensed oxygen level(s), and related systems.